Dust in the Wind

Dust in the Wind: Fallout from Africa may be
killing coral reefs an ocean away

Coughing her way downriver
on a slow boat to Timbuktu, Ginger Garrison is a little out of her element. As
Bozo tribesmen pull catfish from the Niger River and boatmen pole their dugout
canoes through the midday gloom, the strong winter wind known as the harmattan
lifts clouds of fine red dust into the air, and into the eyes and lungs of
people throughout the dry North African region known as the Sahel.

The only breathing
difficulty Garrison, a marine ecologist, usually has to worry about is emptying
her scuba tank too fast in the gin-clear, bathtub-warm waters of Virgin Islands
National Park in the U.S. Virgin Islands. Garrison, a U.S. Geological Survey
(USGS) researcher whose work has focused for nearly 20 years on Caribbean coral
reefs, has come here to Mali seeking a source of one of the most widespread
ecological collapses ever documented.

An ocean away from the
Sahel, coral reef ecosystems around the Caribbean are dying, and scientists are
beginning to think that dust from Africa is playing a major role in their
collapse. Overfishing, sedimentation, and direct damage from boats and divers,
among other threats, have combined with pathogens, climate changes, and
hurricanes to severely degrade reefs around the region. Diseases and bleaching
have decimated once-dominant species like staghorn and elkhorn corals,
longspine sea urchins, and sea fans. Few species or sites have recovered, and
carpets of algae-flourishing in the aftermath of overfishing and die-offs of
sea urchins and other algae-eaters-now dominate many Caribbean reefs.

Yet researchers remain
puzzled by the decline of reefs in apparently pristine stretches of the
Caribbean, far from the usual suspects behind coral decline. "We really don't
understand why this is happening on a regional level, and it's happening not
only in areas where there are a lot of people, it's also happening on remote
reefs. Why?" asks Garrison.

Ever since Charles Darwin
noted "the falling of impalpably fine dust" while crossing the Atlantic during
his famous scientific voyage aboard the Beagle, seafarers and researchers have
observed African particulates far out to sea. But most studies of atmospheric
dust have focused on its potential impacts on the global climate. Only recently
have researchers begun exploring the possibility that the hundreds of millions
of tons of African topsoil blown by prevailing winds to the Caribbean each year
might be having direct, harmful effects on ecosystems and people there.

Dust reaching the opposite
shore of the Atlantic is nothing new. Haze from the Sahel occasionally reduces
visibility and reddens sunsets from Miami to Caracas, and is the source of up
to half the particulates in Miami's summertime air. Pre-Columbian pottery in
the Bahamas is made of windborne deposits of African clay; orchids and other
epiphytes growing in the rainforest canopy of the Amazon depend on African dust
for a large share of their nutrients.

Joseph Prospero of the
University of Miami has tracked dust falling on Barbados, at the far eastern
edge of the Caribbean, since 1965. He discovered a sharp increase in dustfall
around 1970, coinciding with the onset of prolonged drought in North Africa.
The changed African climate, combined with widespread overgrazing of livestock
and the spread of destructive, often export-oriented farming practices in the
Sahel, were sending vastly greater quantities of exposed soil into the sky. In
peak years, winds now drop four times more dust on Barbados than they did
before 1970. Satellite photos of the largest dust event ever recorded, in
February 2000, show a continuous dust bridge connecting Africa and the
Americas.

In the late 1990s, Gene
Shinn and other researchers with USGS noted that benchmark events in the
prolonged, Caribbean-wide decline of coral reefs-like the arrival of coral
black band disease in 1973, mass dieoffs of staghorn and elkhorn corals and sea
urchins in 1983, and coral bleaching beginning in 1987-occurred during peak
dust years.

Researchers have since
found a variety of live bacteria and fungus in dust hitting the Caribbean,
defying conventional wisdom among microbiologists that microbes could not
survive a five-day trip three miles up in the atmosphere. "Swarms of live locusts
made it all the way across alive in 1988 and landed in the Windward Islands,"
Shinn says. "If one-inch grasshoppers can make it, I imagine almost anything
can make it." A 2001 study by USGS researchers found that the number of viable
fungus and bacteria in Caribbean air is two to three times higher during dust
events than during normal weather conditions.

Although the vast majority
of diseases afflicting coral have not been identified (beyond descriptions of
the symptoms they cause), scientists have linked dust to at least one specific
coral-killing microbe. Garriet Smith and colleagues at the University of South
Carolina have identified the pathogen behind the mass die-offs of sea fans, the
graceful soft corals of the Caribbean, as Aspergillus
sydowii-a soil fungus that does not reproduce in salt water. In the very
first sample of airborne dust from the Virgin Islands that Ginger Garrison sent
to Smith, he found live Aspergillus
sydowii in its pathogenic form, among many other microorganisms. The fungal
disease may also enter the sea in local runoff from deforested areas, but dust
studies have established African dust storms as its most plausible source on
isolated reefs and near small islands with no forests and little runoff.

In addition to carrying
living hitchhikers, clouds of African dust bring intense pulses of nutrients
like iron and nitrates that may be stimulating harmful algal blooms and the
rapid growth of both coral-smothering algae and microbes that cause coral diseases.
Microbiologist Hans Paerl of the University of North Carolina calls the
dust-composed of aluminum, silicon, iron, phosphates, nitrates, and
sulfates-"Geritol for bugs."

The dust is not so healthy
for humans, if only because the fine particles irritate the respiratory tract
and can lodge themselves deep in lung tissue. Researchers have barely begun
looking into the health effects of overseas African dust but already have some
provocative findings. For example, they have found pesticides banned for use in
the United States mixed in with dust particles too small for human lungs to
expel. "When they have locust plagues in Africa, we get chlordane and DDT that
we can't use here anymore, but it comes back to us on the wind," Shinn says.

There may be other
unhealthy substances adhering to the particles as well: some studies suggest
the dust carries high concentrations of beryllium-7, a radioactive isotope that
appears to adhere to dust particles as they travel through the atmosphere. While
seeking medical care for her respiratory tract infection in Mali's capital of
Bamako, Ginger Garrison asked around and found that lung problems are terribly
common in Mali during the dust season. After the seasonal floods of the Niger
River recede and its banks dry, mud-mixed with raw sewage, human and animal
waste, and miscellaneous garbage left behind-turns to dust. "Microbes,
synthetic organics, pharmaceuticals, antibiotics, you name it," Garrison
explains. "Then the winds come, and it's a perfect avenue to take those
substances aloft, often north toward Europe or west toward the United States."
She also observed the ubiquitous garbage burning and wonders what carcinogens,
endocrine disrupters, or heavy metals from garbage burning might also find
their way into the atmosphere with dust. She hopes to set up a second
monitoring station near Bamako to look for heavy metals and synthetic chemicals
like DDT, in addition to the station she set up in late 2000 for monitoring
microbe levels in dust.

Africa is not the only
source of dust that affects faraway places. Nutrients from the deserts of
northwestern China sustain Hawaiian rainforests growing on weathered soils.
Chinese haze has long afflicted residents of Japan and Korea, where the yellow
dust, laden with pollutants picked up from Chinese cities it passes over, is
called "the gate-crasher of Spring." South Korean officials suspect that the
dust may have been the source of a recent outbreak of foot-and-mouth disease
among cattle along Korea's west coast. Last Spring, Korea suffered through 20
days of unhealthy haze from abroad, the longest yellow dust spell there in 40
years. Chinese dust even caused hazy sunsets around the western United States
for several days in April 2000. The Chinese, Japanese, and South Korean
governments have launched a program to revegetate dust-generating lands in
China, and researchers from around the Pacific Rim have begun intensive studies
of Chinese dust and its impacts.

To date, the dust blowing
from Africa-unlike Chinese dust-has attracted little attention as a public
health issue. The desertification (severe degradation of arid and semi-arid
lands) that exacerbates dust formation also has serious economic and human
consequences close to home: one in six people in Mali have become environmental
refugees, forced to leave their land as it turns to dust. Despite the massive
amount of land claimed by expanding desertification each year, the phenomenon
receives only infrequent attention, perhaps because the effects seldom seem to
transcend international borders. These new studies of well-traveled dust may
turn that impression on its head.

Given all the locally
generated pollution in the Caribbean, it's understandable that African dust is
on few people's radar screens. But reversing the decline of the region's once
flourishing underwater ecosystems may be impossible without investing more effort
in stabilizing the wind-whipped lands of northern Africa.

"It's just another example
of how small the Earth is, and how so many things are interconnected: global
processes mixed up with how people live their lives," says Garrison. The
mounting evidence of damaging fallout thousands of miles from sources of dust
may help convince the rest of the world to pay more attention again to the
forgotten, dusty corners of planet Earth. "Maybe we're not quite as isolated as
we thought from areas with major health problems," says Garrison. "And maybe we
should be more concerned about the welfare of people and the land in these far
away places."

Former Worldwatch Institute researcher John C. Ryan is a Fellow of
the New America Foundation and author of State of the Northwest 2000.